The present invention relates generally to agents useful in partitioning and/or purification of reactants, intermediate products, and final products from a phase as well as methods of using partitioning agents to selectively separate active agents (either reactant or product) from a phase. The present invention may also be described as being directed to chemical product isolation, separation, phase transfer, and/or purification as well as agents or compounds useful therefor.
An important part of any synthesis or natural product isolation procedure is the separation of a desired compound from contaminants. This step is often the most labor intensive, energy demanding, environmentally abusing, and expensive part of a chemical synthesis or chemical manipulation. Contaminants may include solvents, reaction byproducts, catalysts, reagents, and any other material not required for, or undesirable in, further uses of the product. Both fine chemical synthesis and larger scale chemical production involve at least two essential activitiesxe2x80x94chemical reaction to create the product, and separation (most often for purification purposes) of the product by removing contaminants.
Separations generally rely on phase changes or phase transfers. Distillation, sublimation, solvent evaporation, chromatography, acid-base extraction, solid-solid and solid-liquid extraction, and recrystallization are examples of traditional means of product isolation.
A more recent and currently popular approach to product isolation is based on solid-phase synthetic principles. Generally, solid phase synthesis involves attaching a reactant to an insoluble substrate and allowing reagents to react with the reactant at the surface of the solid. Often beads composed of polymers are used for this process. This method allows the use of large excesses of reagents and catalysts because product separation is achieved by filtration or washing of the solid support. High chemical conversion can be achieved when excesses of reagents are used. However, solid phase synthesis does not have universal applicability. One disadvantage of solid phase synthesis is that reactions at the solid-liquid interface are not always readily controlled. Additionally, not all chemical reactions are compatible with this method, and since solid phase separation is substantially heterogeneous, the use of solid phase synthesis runs contrary to a more preferred homogenous reaction mixture.
Homogeneous reaction mixtures are desirable because reaction conditions can be reliably controlled. A primary disadvantage of homogeneous reactions, and one that solid phase synthesis attempts to avoid, is that contaminants are in the same phase and intimately mingled with desired products or intermediate materials. Products, whether they be final or intermediate stage products, have traditionally been precipitated by removing solvent or by changing solvent, and by covalent or ionic modifications of the product through addition of more chemicals (for example, acids, bases, or metals). Changes in solubility caused by salt formation or protonation or deprotonation can support liquid-liquid extraction approaches to product separation.
Yield, feasibility, and practicality of nearly every reaction is limited by the ability to separate and recover pure product from the reaction mixture. Thus, synthesis and separation are inseparable. Advances in the field of separation have enabled modern synthetic chemists to contemplate and then synthesize molecules of remarkable complexity. At the same time, the power of modern separations has instilled a certain degree of complacency. On the process-chemistry front, one is expected not only to synthesize the desired compound, but to synthesize it cheaply, efficiently, and safely. Furthermore, the advent of combinatorial chemistry has resulted in an expectation that everything can be synthesized quickly. Synthetic chemists have begun to formulate strategic plans for separation at the beginning of a synthesis. In these plans separation dictates synthesis and molecules in the final reaction mixture are designed to virtually separate themselves when processed in a purification stage. These plans rely on relatively simple workup techniques such as evaporation, extraction, and filtration.
Four phases are commonly used in standard laboratory separation methods: a gas phase, a solid phase, and two liquid phasesxe2x80x94organic and aqueous. A third liquid phase known as a xe2x80x9cfluorousxe2x80x9d phase has recently found applicability in organic synthesis. Among the phase separation techniques, liquid-liquid extractions play an important role in the purification of organic compounds. These extractions are almost always conducted with an organic solvent and water. Most frequently, they are used to separate organic compounds from inorganic compounds. A less frequent but still important application of organic-water extractions is an acid-base extraction. Yet another common technique used for separation is chromatography. Chromatographic methods of purification are immensely important, yet they are also expensive and time consuming. A recent review of issues and approaches to product isolation and extraction is provided in xe2x80x9cStrategy-Level Separations in Organic Synthesis: From Planning to Practice,xe2x80x9d D. P. Curran, Angewandte Chemie Int""l Ed. Engl., 1998, v 37, 1174, which is hereby incorporated by reference thereto in its entirety.
The present invention is directed to a separation technique and agents useful therefor. As will be described more fully herein, the present invention allows for selective isomerization of a chemical moiety removably attached to a product or intermediate for selective separation of product or the intermediate by phase change or transfer.
Specifically, compounds described herein comprise a reactant isomer functionalized for attachment to a reactant molecule, the reactant isomer capable of being isomerized into a separating isomer, the separating isomer having a different solubility than the reactant isomer. The compound or compounds generally are of the following formula 
wherein R11 and R12 are each independently the same or different, a hydrogen, a halide, OR, OH, OOH, OOR1, SR1, CN, NC, NR1R, a linear or branched alky group, an aryl group, a phenyl group, a substituted aryl, a substituted phenyl group, or other common functional group.
Another embodiment of the present invention is a compound of the following formula 
wherein L is a linking group, the linking group being capable. of isomerization and R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are, each independently, the same or different, a halide, OR, OH, OOH, OOR1, SR1, CN, NC, NR1R, a linear or branched alky group, an aryl group, a phenyl group, a substituted aryl, a substituted phenyl group, or other common functional group. Further, it is preferable that the reactant isomer be a cis-alkene and the separating isomer be a trans alkene. The separating isomer may also be a geometrical isomer, a stereoisomer and/or a structural isomer.
A method of separating a desired product from a reaction mixture is also disclosed wherein the method is comprised of covalently linking a separating agent to a reactant molecule, reacting the so formed reactant molecule to form a product with the separating agent being attached to the product, isomerizing the separating agent to thereby form a separable form of the product, and separating the product from the reaction mixture. The method further includes the step of cleaving the separating agent from the product to thereby form a purified product. Isomerization may occur through geometrical isomerization, stereoisomerization, and/or structural isomerization. Preferably, in this embodiment, the modified reactant molecule may be selectably transferred from one phase (e.g., hydrophobic) to another (e.g., hydrophilic) by isomerization.
The phase partitioning agent may also be of the general formula: 
wherein L is a linking group, the linking group being capable of isomerization and R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are, each independently, the same of different, a halide, OR, OH, OOH, OOR1, SR1, CN, NC, NR1R, a linear or branched alky group, an aryl group, a phenyl group, a substituted aryl, a substituted phenyl group, or other common functional group. Some useful phase partitioning agents are represented below: 
Another aspect of the present invention is a method of partitioning a reactant from a phase comprising isomerizing a precipiton covalently linked to the reactant. The step of isomerizing the precipiton may include adding a chemical isomerizing agent and in a preferred embodiment irradiating the precipiton. In addition the reactant may have a plurality of precipitons attached to the reactant with each of the plurality of precipitons individually and selectively isomerizable.
The term xe2x80x9creagentxe2x80x9d as used herein refers to a chemical entity that is required for a reaction but contributes either an invariant piece or no piece to the products of a synthesis. As used herein, the term xe2x80x9creagentxe2x80x9d includes a catalyst or any agent that is necessary to the chemical reaction but is itself substantially unchanged during the chemical reaction, whether or not it is used in substoichiometric quantities.
The term xe2x80x9creactantxe2x80x9d as used herein in connection with synthesis refers generally to a type of molecule that contributes a variable piece to the products of a synthesis. The distinction between the terms xe2x80x9creactantxe2x80x9d and xe2x80x9creagentxe2x80x9d in xe2x80x9ccommonxe2x80x9d (non-combinatorial) organic syntheses is vague, but those skilled in the art often refer to a reaction component as a reagent if it contributes no piece, a rather small piece, or a piece without carbon atoms therein to the target product.